The field of invention is minimally invasive vascular surgery, and more specifically an apparatus and method for occluding a blood vessel with clips applied with an applicator extending through a cannula.
Minimally invasive surgery has grown in popularity in the past decade. Minimally invasive surgery (MIS) allows a surgeon to treat a patient while making only tiny incisions in the patient's body, through which surgical devices called cannulae are inserted. A cannula is essentially a thin, hollow tube through which other surgical tools can be inserted into and withdrawn from the patient's body. Because only a small incision is made in the patient's skin for insertion of a cannula, the patient heals faster and experiences less pain than in the aftermath of conventional surgery, in which larger incisions and tools are used.
In several minimally invasive procedures, blood vessels in a patient are permanently occluded. Two common procedures involving blood vessel occlusion are saphenous vein harvest, in which a vein and its branches are occluded so that a portion of that vein can be removed from one location in the body and used in another, and subfascial endoscopic perforator surgery, in which perforator veins are permanently occluded. In recent years, malleable metal clips have been used for permanent occlusion. These clips typically have an opening at one end that is at least as wide as the blood vessel to be occluded. A surgical instrument is inserted through the cannula which places these clips, often serially, in desired locations on blood vessels, then squeezes them shut to achieve permanent occlusion. Such surgical instruments have in the past been bulky enough to require a cannula having an internal diameter of 10 mm or even 12 mm in order to insert them through the cannula to reach the operative site. However, it is often desired to occlude blood vessels having a diameter of 5 mm or less. Ideally, a cannula having an internal diameter of substantially 5 mm would be utilized to occlude a blood vessel having a diameter of 5 mm or less, because the use of a 5 mm cannula is less invasive and traumatic to a patient than a 10 mm or 12 mm cannula. But, as stated above, known surgical instruments for applying blood vessel clips are too large to fit into a cannula having a 5 mm internal diameter, thus requiring the patient to suffer through insertion of a larger-than-optimal cannula for occlusion of blood vessels having a diameter of 5 mm or less.
In addition, malleable blood vessel clips known in the art can rebound after they have been squeezed shut over a blood vessel. Malleability requires that the metal of the clip be in a relatively annealed state, or at least possess adequate elongation to remain intact without cracking or breaking when deformed to achieve closure over the blood vessel. Annealed metal is relatively soft, and this softness is beneficial in that it allows for extreme elongation when substantially annealed metal is shaped into a blood vessel clip. When a malleable clip is closed by a tool, that clip is typically bent in a fashion that causes permanent deformation. Upon removal of the tool, the bent portion of the clip is released. However, the elasticity of the annealed clip can cause it to open slightly upon release of the tool, as the stress in the bend resolves to a net-zero stress condition. Loads placed on the clip, such as the loads exerted by the blood vessel within the clip, serve to increase this rebound. Clip rebound tends to allow opening of the blood vessel, reducing the degree of occlusion. Rebound can thus result in leakage through the vessel, which is undesirable. This rebound increases as the metal in the blood vessel clip is less annealed. Multiple malleable clips may be placed over a single blood vessel to ensure continued occlusion of the blood vessel. However, placement of multiple clips requires additional surgical time and expense.